(1) Field of the Invention
This invention concerns a trench located in a landfill including the combination of a liquid infiltration piping system and a horizontal gas withdrawal piping system that allows for simultaneous liquid infiltration and gas withdrawal. The trench of this invention can be retrofit into existing landfills or they can be incorporated into landfills as the landfill is being constructed.
(2) Description of the Art
The recovery of landfill gases including light hydrocarbons such as methane has become commonplace and is regulated under New Source Pollution Standards (NSPS). It used to be common to burn gasses vented from landfill. However, it is becoming more common to use landfill gases to generate heat and or electricity.
Landfill leachatexe2x80x94the aqueous solution that accumulates at the bottom of landfills also poses disposal and odor problems. One method for dealing with leachate odor problems that is gaining wide acceptance is to pump the leachate from the bottom to the top of the landfill to allow the leachate to percolate though the landfill where biological material in the leachate provide nutrition source for microorganisms that remediate the leachate. The recirculation of landfill leachate has led to the conversion of areas of landfillsxe2x80x94known as cellsxe2x80x94into anaerobic or aerobic bioreactors. The normal biological degradation of organic landfill materials can be dramatically accelerated in bioreactors resulting in the creation of more landfill airspace thereby extending the useful landfill life.
The prior art discloses several methods for withdrawing gas from landfills. EU Publication Number 036508B1 discloses a method of controlling the recovery of landfill gas from a sanitary landfill by measuring the temperature of the gas and adapting the gas withdraw according to the temperature measurements. A similar landfill monitoring and control system is disclosed in U.S. case 2001/0005812 A1.
European Patent Application No. 0505218 A1 discloses concrete components including elongated hollow cylindrical piles that are installed in landfills in order to remove landfill gases. The disclosed piles are designed to be vertically orientated in a landfill.
U.S. Pat. No. 6,334,737 discloses a method of controlling landfill gas generation within a landfill in which leachate is recycled and continuously injected into the landfill while extracting the landfill gas from a landfill gas extraction pipe inserted into the waste.
U.S. Pat. No. 6,283,676 discloses a landfill including multiple lifts having horizontal piping layers and the methods for their use to accelerate anaerobic and or aerobic degradation of municipal solid waste in order to increase landfill capacity.
The combination of leachate recirculation and gas extraction of landfill has created a problem with gas extraction well flooding and fouling. To avoid flooding, the leachate is typically supplied in horizontal pipes while gas is extracted from the landfill in the region of lechate infiltration in vertical piping. This requirement for both vertical and horizontal piping in the landfill makes installation difficult and expensive. There is a need therefore for landfill gas extraction that are easier cheaper to construct and that use horizontal gas extraction piping systems.
One aspect of this invention is a landfill trench comprising; a bottom material; at least one horizontal gas collection pipe; at least one liquid distribution pipe; a cover material; and a filler material located between the bottom and the cover material.
Another aspect of this invention is a landfill having a plurality of trenches, each trench comprising a bottom material; at least one horizontal gas collection pipe; at least one horizontal liquid distribution pipe; a cover material; and a filler material located between the bottom and the cover material wherein the landfill further includes a gas piping header and a gas riser that unites the horizontal gas collection pipes of each of at least two trenches with the gas header, and a liquid header wherein a liquid riser unites the liquid header with each horizontal liquid distribution pipe.